I have been three times, each time I have done it differently. Tickets from the ceremony should be purchased as soon as you commit to going, although you can get tickets on the secondary market and on the street as you get closer to the stadium. Another option if you wish to continue your tailgating (no alcohol inside the stadium) is to park on the lawns/homes across from the stadium. People will let you park and just sit with your cooler and lawn chairs and watch the whole scene through the fences. For a first time, I would go inside, but if you have been a few times, and you want to enjoy a few adult beverages, this could be an option, just set yourself up beforehand, if you are near the stadium earlier in the day, make plans with the owners, they can be very accommodating.
I have not done the full packages, the parade is free, and when a Bills guy goes in, the Bills fans tailgate anyway, so we usually end up wherever they are.
Hotels are usually at a premium. If you haven't already started looking, get moving, the closer you are, the more it will cost. We have found cheaper options in Alliance and New Philadelphia that were under 100 per night and usually there are plenty of Bills fans around.
If you get into town early, go to the hall Friday, Saturday it is very crowded and stuffy, but on Saturdays you will run into former players ( I stood in line behind Deacon Jones at the gift shop a few years ago). On Saturday they have merchandise/memorabilia tents and activities behind the Hall that they have signings and goods for the incoming players.